Half Shaft Modifications
This section has been a late entry into the information put on this disk. The reason being that after I had written all the other sections upon completion of the car, I found weak links in the cars driveline, as brought out under the severe stresses produced in a racing environment.
The following was written after 3 races, of which the car broke during 2 of these races with sheared U-joints on the Z half shafts. The U-joints held up for most of the races, and on the last failure, it sheared in two as I was crossing the finish line. I had installed Spicer U-joints in the half shafts, under the advice that these were the strongest joints available ( I feel the original Datsun joints were probably stronger, but when I went to the dealer to buy new ones at double the price of the Spicers, I found that the old part number refers to a new number, and the new joints do not look as beefy as the original ones did, So I went with the Spicers). Being the Spicers strength should be able to handle the V-8 torque easily, I would probably stick with the Spicer equipped U-joints if the geometry of the half shafts was ideal, but it's not. What I am writing about here is that, with the chassis lowered to it's present competition ride height, the geometric relationship between the differential and the wheel axles has drastically changed to the point that the differential now hangs a good bit lower than the wheel axles . This then brings about a problem of having a lot (approximately 8 degrees) of angularity in the U-joints even at the static ride height. This amount of misalignment, I've been told, is about the limit that U-joints can be expected to reliably hold up to during heavy torque loads. But now, compound this problem with the squatting effect of the rear of the car during heavy acceleration and during bumps on the racing surface (which in effect increases the misalignment even more to approximately 12 degrees or more), and you have a setting for a failure. I knew, during the building of the rear part of the car, that the half shafts would not exit the differential or wheel axles in perfect alignment because of the lowering of the car, so to help improve the situation, I raised the differential as high as possible (approximately 1 inch) without cutting into the rear cross brace over the differential case. But this now still appears to be insufficient for racing. The conclusion I came to after discussing my U-joint problem with a number of people who have raced Z-cars successfully is that my U-joint problem is not so much a factor of the strength of the joints, but instead a function of the adverse angles with which they are operating in.
To remedy the above problem, I can take two routes. One is to raise the ride height at the rear by an amount to keep the half shafts more perfectly aligned during racing conditions, which would be about 1-1/2", or the other remedy is to go with constant velocity joints, which can handle a misalignment limit of about 15 degrees and still be fairly reliable.
I chose to do both. I raised the car by about, and then proceeded to find a means of putting CV joints in the back. The first idea I used was to use VW bus or bug CV joints. This was because these joints are strong, easily removed/replaced, cheap, and can be adapted to the Datsun easily. The second idea was to find a Datsun setup that would fit. Being I chose to go with the Datsun parts even after already doing all the work with the VW parts, I will discuss the Datsun swap first.
Datsun CV joints
I chose to fabricate a bushing to be placed into the Z wheel bearing housing, and then place the ZX grease seal inside this bushing. This bushing was made by cutting 3/8" thick rings off of a section of 2-1/2" schedule 40 steel pipe. The outside diameter of these rings is a tad bit to large to fit into the Z wheel bearing carrier, so I split the rings at a single location by cutting out a piece of the ring. Then I compressed the ring evenly all the way around its circumference to close up the gap, that I had previously cut in it, to about 1/16", thus reducing the overall O.D. of this ring (bushing). Then I lightly chamfered the circumference of the ring. The ring can now be lightly pressed into the wheel bearing housing, into the location where the original Z grease seal used to be, thus closing the gap in the ring completely as the ring (bushing) is "squeezed" into the wheel bearing carrier (this is why I chamfered the rings, so as to allow them to be started easily into the housing). I found out through trial-and-error that the best way to install the grease seal into this bushing, is to first place the seal into the bushing before you press the bushing into the housing. This way the ring will compress around the seal, thus providing a good strong hold on the seal. I also used a small amount of gasket sealer at the ring gap and the outer circumference of the ring to seal the bearings completely from any dust and dirt.
The complete Turbo half shaft assembly in the installed position will be the same length as the stock Z half shaft, BUT un-installed, the Turbo shaft appears to be too long. This is because the casing holding the CV joints are spring loaded at the wheel end, making the shaft appear to be longer than the installed length will be. As you will see, the spring is fairly soft and can be totally compressed by hand to fit correctly, and still allow the shaft about 1/2" of play for suspension movement installed. To install this Turbo half shaft, you will need to temporarily increase the spread between the differential and the strut by (my method) removing the inner lower arm bushing saddles, thus allowing the strut (and attached lower arm assembly) to swing away from the differential. This procedure of spreading the strut away from the differential is needed because even with the shaft fully compressed, there is a convex knob (inside of which holds the spring for the CV joint) on the end of the shaft that fits into the concave companion flange already installed on the axle stub. In order to slip the shaft end into the companion flange you will thus need to gain about an inch extra clearance. Once the wheel end of the shaft is fitted into the companion flange, then the strut can be returned to it's normal position.
Note: In the time since the above information was written, another method of grease seal placement has been found which may be more appealing to the average builder. The R200 differential front pinion grease seal (75mm O.D. X 40mm I.D.) can be made to fit into the wheel bearing housing where the original grease seal fits in the rear struts, thus eliminating the need to manufacture the bushing using a metal pipe ring as discribed above. This new seal must have all the rubber removed from the outer circumference in order to reduce the O.D. to its minimum (about 73mm). Even with this outer layer of rubber removed, there will be an abnormally large interference fit which will make it difficult to install. I then chamfered the outer edge of the metal lip of the seal to facilitate it's installation, which was done by carefully tapping the seal into the strut bearing carrier with a large flat doughnut shaped plate used as a mandrel to allow even pressure to be applied to the entire seal as it is tapped or pressed into the carrier (be sure to use a small amount of sealant such as silicone to make this a water tight seal). One might even be able to use the axle stub threads and nut to press (draw down) the seal into the carrier with an appropriate shaped plate. Anyway, this pinion seal will simplify the grease seal problem by eliminating the need for manufacturing the metal bushing out of the pipe ring mentioned earlier to hold the ZX seal.
Also, the small dust shield that is pressed onto the ZX companion flange piece to keep dust and dirt away from the grease seal was swapped with the dust shield from the comparable Z piece. This was done to maintain a better shield due to the different designs. I did this by cutting the tack welds on the Z piece, I then pressed the shield off. Then, after I pressed the dust shield off the ZX piece, I placed it onto the Z piece and then permanently tack welded it on .
I wished I had found this swap prior to all the work and expense of the previously mentioned VW parts swap, but I still feel the VW setup is ultimately the strongest of the two. But for now, I will use the Datsun CV setup and see if it will hold up to the rigors of racing. The ZX swap cost me about $100 verses the $400 for the VW swap (thats in salvage dollars).
Note: when removing the wheel bearing retaining nut off the Z cars (to remove the wheel bearing companion flange), the threads on the axles will be damaged if the nut is not removed with care, due to the peening that is done to the nut to prevent it from working loose. Fortunately, this same nut on the ZX cars is just a regular lock nut (same threads as on the Z too), BUT, bring some help to break it loose. After using an impact wrench and then a drive ratchet with no luck, I finally had to use a "come-along" attached from the breaker bar handle to the car chassis to finally break it loose.
Important note: I recieved some feedback from a gentleman in Detroit that was performing this modification on a 260Z. It seems that his axle stubs in the 260Z struts were 26 spline stubs (whereas the my 240 axle stubs are 25 spline) with a slightly larger diameter that the 240 stubs. Thus the ZX companion flange would not slide on (This was double and triple checked and later compared to the 240 stubs and verified). Make certain you obtain the 25 spine axle stubs in the struts, or this modification will not work (In other words, make sure the Turbo companion flanges will slide onto the splines of the axles you will be using!).
*There are some important differences in the CV jointed half shafts for the 280ZX and the 300ZX. I will briefly list them so that replacement parts or salvaged parts might be found easier. From the data found in a CV joint rebuild guide that I was able to look through, I found that all the '82-'83 280ZX Turbo's and some of the 2+2's use the same exact half shaft. These half shafts use a "tripode" design in the CV joints, meaning they have a 3 pronged (120 degree), needle bearing equipped joint. The axles themselves are 14-11/16" long, both left and right sides, and have 27 tooth splines at both ends. All other 280ZX's use the U-joint type of half shafts. The differential axle stub assembled as part of the shaft has 25 teeth in the splines that will fit into the R200 "Z" differential.
The '84-'89 non-turbo 300ZX half shafts are almost the same as the 280ZX shafts, except that the axle lengths are 15-3/4" long for the right side, and 15-3/8" long for the left side, but the ends of the axles themselves have the same 27 tooth splines. If worst came to worst, I would check your specific car's dimension to see if there is enough lateral movement in the CV joints to be able to use these longer axles, without any binding, provided you changed the inboard differential axle stub part. The differential axle stub is assembled as part of the inner joint, and has a different set of splines than the 280ZX, so this end won't interchange either. But, the good news is that the tripod assembly itself, that fits on the ends of the axle splines, are the same between the 280ZX and the 300ZX shafts. On the turbo versions of the 300ZX, Nissan went to a more traditional ball-and-cage version of the CV joints used on these half shafts, with no interchangability of their parts.
VW bug & bus CV joints